Document [1] “Motorola Document Number S12SPIV3/D—SPI Block Guide V03.06—Original Release Date: 21 Jan. 2000—Revised: 4 Feb. 2003” describes a serial communication system and protocol called Serial Parallel Interface (SPI). SPI allows a duplex, synchronous, serial communication between a master serial device (master control unit MCU) and peripheral electronic device, usually called slave device. The slave device has a serial interface unit for communicating with the master device according to the serial protocol via a serial data line and a serial clock line. SPI defines the serial clock line (SCLK), whereas the serial data line may have various functions (MOSI Master Output, Slave Input; MISO Master Input, Slave Output; MOMI Master Output, Master Input; SISO Slave Input, Slave Output).
The serial protocol defines a clock cycle comprising a clock pulse on the serial clock line and a serial data bit value on the serial data line to be communicated synchronously to said clock pulse, and a serial data word transfer comprising a predetermined number of clock cycles for communicating a data word having data bit values.
Both the master device and the slave device have to perform logical operations to function as required. For such operations a clock is required. The operations in the slave device may interact with the operations of the serial interface unit, and therefore must be controlled to be in line with the clock pulses on the serial clock line. While the slave device requires a clock to perform the logical operations, it is relatively complex to provide such a clock to robustly perform such operations.